[M-IS14] Paleoclimatology and paleoceanography

[MIS14-P14] Reconstruction of bottom-water oxygenation changes during the Younger Dryas based on benthic foraminiferal assemblages off Shimokita in the western North Pacific

*Fumiya Maruta¹, Yusuke Okazaki¹, Kana Nagashima², Takuya Sagawa³, Takuto Kasuya¹, Wei-Cheng Hsiung¹, Yusuke Yokoyama⁴, Yosuke Miyairi⁴, Katsunori Kimoto² (1.Kyushu University, 2.Japan Agency for Marine-Earth Science and Technology, 3.Kanazawa University, 4.The University of Tokyo)

Benthic foraminifera are suitable for monitoring the oxygen level of the bottom water because of their rapid responses to changes in dissolved oxygen. Ice sheets covered the northern part of North America and Eurasia during the last glacial period from 100 ka to 20 ka. After that, the ice sheets retreated during the last deglaciation from 20 ka to 7 ka with abrupt millennial-scale climate changes. Among them, the Younger Dryas (12.9 ka – 11.5 ka) was a remarkable cold event in the Northern Hemisphere. The trigger of the Younger Dryas event was the massive meltwater from North America to the North Atlantic, which hampered thermohaline circulation. The Younger Dryas event was observed in the Northern Hemisphere. In the western North Pacific off Shimokita, millennial-scale changes in the sedimentary faces were found during the last deglaciation, laminations during the Bølling-Allerød, 14.5 ka- 12.9 ka, and the Preboreal, 11.5 ka- 10.5 ka around the time of the Younger Dryas. These suggest drastic changes in dissolved oxygen conditions on the seafloor off Shimokita, i.e., dysoxic during the Bølling-Allerød and the Preboreal, whereas oxic during the Younger Dryas. In this study, we investigated the benthic foraminiferal assemblages from the Younger Dryas to Preboreal intervals in the SMK3-PC piston core (41°08.53'N, 142°24.58'E, water depth 1356 m) from off Shimokita obtained during the MR23-05 cruise of the R/V Mirai. Oxic ([O2] > 1.5 mL/L) taxa dominated during the Younger Dryas, and dysoxic ([O2] = 0.3-1.5 mL/L) taxa dominated during the Preboreal. Suboxic taxa ([O2] = 0.1-0.3 mL/L) had a relative abundance peak during the transition from the Younger Dryas to the Preboreal. These changes in benthic foraminiferal assemblages suggest an oxic seafloor condition off Shimokita during the Younger Dryas due to low surface water productivity.